Consider that we see this story in flashback form, that Sisko is actually telling it to the Temporal Investigations guys. Yet one of his lines during the episode is that he doesn't want a visit from Temporal Investigations when he gets home. Doesn't this seem like a rude thing for him to tell them?

At one point Bashir comments that surely O'Brien must have taken Elementary Temporal Mechanics at the Academy. Well, no - O'Brien's an enlisted man, he never went to the Academy.

Much comment was prompted amongst fans by the scene in which Bashir and O'Brien are all confused about why Klingons had no head ridges in the TOS timeframe. Worf refuses to comment, stating that they do not discuss it with outsiders. Enterprise would later reveal that the change was a result of a virus which infected the Klingon population, and was then cured by a genetic change created by Phlox which erased the head ridges as a side effect. So... given that Humans clearly knew that Klingons originally had ridges, and Humans were directly involved in the situation which resulted in their removal... why isn't this common knowledge in the 24th century? Surely at the very, very least it would be something that a Doctor like Bashir would know about.

Great Moment :

Dax in a TOS miniskirt!

Plotline

Thrown back in time by a Klingon intelligence officer in Human guise, the Defiant crew find themselves nose to nose with the original Starship Enterprise. Now they must race against time to recapture the Klingon before he can alter the timeline by assasinating one Captain James Tiberius Kirk.